Estimated regional CO₂ flux and uncertainty based on an ensemble of atmospheric CO₂ inversions

Global and regional sources and sinks of carbon across the earth’s surface have been studied extensively using atmospheric carbon dioxide (CO2) observations and chemistry-transport model (ACTM) simulations (top-down/inversion method). However, the uncertainties in the regional flux (+ve: source to the atmosphere; −ve: sink on land/ocean) distributions remain unconstrained mainly due to the lack of sufficient high-quality measurements covering the globe in all seasons and the uncertainties in model simulations. Here, we use a suite of 16 inversion cases, derived from a single transport model (MIROC4-ACTM) but different sets of a priori (bottom-up) terrestrial biosphere and oceanic fluxes, as well as prior flux and observational data uncertainties (50 sites) to estimate CO2 fluxes for 84 regions over the period 2000–2020. The ensemble inversions provide a mean flux field that is consistent with the global CO2 growth rate, land and ocean sink partitioning of −2.9 ± 0.3 (±1σ uncertainty on mean) and −1.6 ± 0.2 PgC yr−1, respectively, for the period 2011–2020 (without riverine export correction), offsetting about 22–33 % and 16–18 % of global fossil-fuel CO2 emissions. Aggregated fluxes for 15 land regions compare reasonably well with the best estimations for (approx. 2000–2009) given by the REgional Carbon Cycle Assessment and Processes (RECCAP), and all regions appeared as a carbon sink over 2011–2020. Interannual variability and seasonal cycle in CO2 fluxes are more consistently derived for different prior fluxes when a greater degree of freedom is given to the inversion system (greater prior flux uncertainty). We have evaluated the inversion fluxes using independent aircraft and surface measurements not used in the inversions, which raises our confidence in the ensemble mean flux rather than an individual inversion. Differences between 5-year mean fluxes show promises and capability to track flux changes under ongoing and future CO2 emission mitigation policies.

Phthalates, non-phthalates, polychlorinated biphenyls and phenyl phosphates in atmospheric suspended particulate matter of Dhahran City, Saudi Arabia: Levels and seasonal variation

This work describes the seasonal variations, levels, and possible health effects of groups of persistent organic pollutants (POPs) as phthalates (Ps), non-phthalates (NPs), polychlorinated biphenyls (PCBs), and phenyl phosphates (PhePhs) in ambient total suspended particles (TSP) from the city of Dhahran, Saudi Arabia. The mass concentrations of TSP ranged from 88±32 µg m−3 in winter to 350±320 µg m−3 in summer. The total concentrations of these compounds varied from 337±266 ng m−3 in summer to 469±403 ng m−3 in winter. The major compounds were Ps (235±199 ng m−3 in summer to 389±335 ng m−3 in winter), PCBs (30.7±19.3 ng m−3 in autumn to 65.6±61.2 ng m−3 in summer), NPs (4.9±2.3 ng m−3 in summer to 11.9±12.5 ng m−3 in winter), and PhePhs (4.1±4.0 ng m−3 in spring to 13.3±3.2 ng m−3 in summer). The proportional fractions of these POPs relative to natural biogenic sources and petroleum-related emissions were extremely high ranging from 17% in winter to 47% in autumn. Significant correlations were found among these different POP groups and total concentrations, suggesting that they were from local sources. Principal component analysis indicated that Ps and NPs were from the same initial sources, and the PhePhs as well as PCBs were from different regional sources, where the latter were dependent on the TSP levels. In the long term, the elevated levels of these POPs in the TSP of these urban areas will affect human health by eventually developing a range of illnesses.

The Occurrence of Heavy Air Pollution during the COVID-19 Outbreak in Beijing, China: Roles of Emission Reduction, Meteorological Conditions, and Regional Transport

To prevent the spread of coronavirus disease (COVID-19) and mitigate the epidemic risk, strict lockdown measures were implemented in Beijing during the quarantine period, significantly reducing human activities. However, severe air pollution episodes occurred frequently in Beijing. To explore the occurrence of severe air pollution during the quarantine period, the impacts of emission reductions, meteorological conditions, and regional transport on heavy air pollution were individually evaluated using the Community Multiscale Air Quality (CMAQ) model. Observations showed that the more unfavorable meteorological conditions which occurred during the pandemic as compared to the corresponding 2019 levels, including higher temperature, relative humidity, and frequency of strong southerly winds, and lower HPBL, led to an increase in PM2.5 concentrations. The model results also showed that the meteorological conditions in February 2020 favored PM2.5 formation. The PM2.5 concentrations were mainly dominated by regional transport, which became more significant in the quarantine period than in 2019, suggesting the importance of joint control on regional sources for reducing heavy air pollution. This study highlights that, although the emissions in Beijing and surrounding regions were largely reduced during the quarantine period, severe air pollution in Beijing did not reduce due to the unfavorable meteorological conditions.

Seasonal predictability of baroclinic wave activity

Midlatitude baroclinic waves drive extratropical weather and climate variations, but their predictability beyond 2 weeks has been deemed low. Here we analyze a large ensemble of climate simulations forced by observed sea surface temperatures (SSTs) and demonstrate that seasonal variations of baroclinic wave activity (BWA) are potentially predictable. This potential seasonal predictability is denoted by robust BWA responses to SST forcings. To probe regional sources of the potential predictability, a regression analysis is applied to the SST-forced large ensemble simulations. By filtering out variability internal to the atmosphere and land, this analysis identifies both well-known and unfamiliar BWA responses to SST forcings across latitudes. Finally, we confirm the model-indicated predictability by showing that an operational seasonal prediction system can leverage some of the identified SST-BWA relationships to achieve skillful predictions of BWA. Our findings help to extend long-range predictions of the statistics of extratropical weather events and their impacts.

A black carbon peak and its sources in the free troposphere of Beijing induced by cyclone lifting and transport from central China

Observations suggest that the vertical distributions of air pollutants, such as black carbon (BC), present as various types depending on the emission sources and meteorological diffusion conditions. However, the formation process and source appointment of some special BC profiles are not fully understood. In this paper, by using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) with a BC-tagging technique, we investigate the formation mechanism and regional sources of a BC peak in the free troposphere observed by an aircraft flight in Beijing (BJ) on 5 May 2018. The results show that the contribution rate of the Beijing–Tianjin–Hebei (BTH) region to the surface BC of BJ exceeded 80 % in this case. Local sources dominated BC in BJ from the surface to approximately 700 m (78.5 %), while the BC peak in the free troposphere (∼4000 m) was almost entirely imported from external sources (99.8 %). Combining BC tracking and process analysis, we find that horizontal advection (HADV) and vertical advection (VADV) processes played an important role in the convergent and upward movement and the transport of BC. The BC originating from the surface in central provinces, including Shanxi (SX), Henan (HN), and Hebei (HB), had been uplifted through a cyclone system 16 h previously, was transported to a height of approximately 3000 m above BJ, and was then lifted by the VADV process to approximately 4000 m. At the surface, BJ and its surroundings were under the control of a weak pressure gradient, leading to the accumulation of BC within the boundary layer. Our results indicate that cyclone systems can quickly lift air pollutants, such as BC, up to the free troposphere, as well as extend their lifetimes and further affect the regional atmospheric environment and climate.

Source Apportionment and Health Risk Assessment of Heavy Metals in PM2.5 in Handan: A Typical Heavily Polluted City in North China

In order to determine the pollution sources and human health risks of metal elements in PM2.5, samples were collected by a large flow particulate matter sampler in the four seasons in 2013, 2015, and 2017 (January, April, July, and October). The mass concentrations of 10 metals (Ti, V, Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) were analyzed. The sources of heavy metals were identified by Unmix, and the potential non-carcinogenic/carcinogenic risk was evaluated. The influences of local and regional sources were also explored during the high-carcinogenic risk period (HCRP). The wind field and 72 h backward trajectories were performed to identify the potential local and regional sources in HCRP. The results showed that the average annual concentrations of PM2.5 in the urban area of Handan city were 105.14, 91.18, and 65.85 μg/m3 in 2013, 2015, and 2017, respectively. The average daily concentrations of the metals in PM2.5 in January were higher than that of April, July, and October. The average mass concentrations of the 10 heavy metal elements in PM2.5 were 698.26, 486.92, and 456.94 ng·m−3 in 2013, 2015, and 2017, respectively. The main sources of the metals in PM2.5 were soil dust sources, vehicular emissions, coal burning, and industrial activities. The carcinogenic risks of Cr and As were above 1 × 10−6 over the three years. Wind direction analysis showed that the potential local sources were heavy industry enterprises and the economic development zone. The backward trajectory analysis indicated that PM2.5 long transported from Shandong, Henan, and the surrounding cities of Handan had quite an impact on the heavy metals contained in the atmosphere of the studied area. The health risk assessment results demonstrated that the trend for non-carcinogenic risk declined, and there was no non-carcinogenic risk in 2017. However, the carcinogenic risk levels were high over the three years, particularly in January.

Regional flow climatology for central Mexico (Queretaro): a first case study

A flow climatology was established for the Metropolitan Area of Queretaro (MAQ), in central Mexico, by analyzing four years (2014-2017) of back-trajectories generated using the HYSPLIT Model. Two flow regimes were found: one from June until September (rainy regime); the other from December to May (dry regime). October and November were considered transition months. Northeasterly flows were present throughout the year; in contrast, trajectories from the southwest were much less frequent and observed mainly during the dry regime. An analysis of the wind fields from the NARR database for a longer period of time (1979 – 2019), suggests that these results are representative of the average conditions of the atmosphere at the study site. Some of the northeasterly trajectories observed originate within a desertic region of the state of Queretaro, where several limestone mines are located. During the dry regime and transition months some clusters originate at the industrial area in Guanajuato, which includes the Salamanca refinery. As air transport of pollutants follow these paths, this analysis could be useful for identifying regional sources that affect the MAQ and possibly increase its air pollution load. In fact, the variability of criteria pollutants concentrations matched the flow regimes described above.

Vulnerability of agricultural households to climate change in hill state of north Western Himalaya

In the present study, vulnerability level of individual farming households to climate change is examined in Himachal Pradesh, North-western state of India. Principal Component Analysis (PCA) was used to develop vulnerability index for individual household. Mean household vulnerability index in the study area was 0.27. The farming households from Kullu district were the most vulnerable (5.94) while those from Hamirpur district were least vulnerable (-3.37). The study successfully identified the regional sources of vulnerability and prioritises the districts for adaptation planning. Implication of the study results lays with the policy makers in formulating region specific and targeted climate adaptation policies that foster asset building so as to reduce vulnerability and build long-term resilience to climate change.

A black carbon peak in the free troposphere of Beijing induced by cyclone lifting and transport from Central China

Observations suggest that the vertical distributions of air pollutants, such as black carbon (BC), present as various types depending on the emission sources and meteorological diffusion conditions. However, the formation process and source appointment of some special BC profiles are not fully understood. In this paper, by using the Weather Research and Forecasting model coupled with chemistry (WRF-Chem) with a BC-tagging technique, we investigate the formation mechanism and regional sources of a BC peak in the free troposphere observed by aircraft flight in Beijing (BJ) on May 5th, 2018. The results show that the contribution rate of the Beijing-Tianjin-Hebei (BTH) region to the surface BC of BJ exceeded 80 % in this case. Local sources dominated BC in BJ from the surface to approximately 700 m (78.5 %), while the BC peak in the free troposphere (~4000 m) was almost entirely imported from external sources (99.8 %). Combining BC tracking and process analysis, we find that horizontal advection (HADV) and vertical advection (VADV) processes played an important role in the convergent and upward movement and the transport of BC. The BC originating from the surface in central provinces, including Shanxi (SX), Henan (HN) and Hebei (HB), was uplifted through a cyclone system 16 hours previously, transported to a height of approximately 3000 m above BJ, and then lifted by the VADV process to approximately 4000 m. At the surface, BJ and its surroundings were under the control of a weak pressure gradient, leading to the accumulation of BC within the boundary layer. Our results indicate that cyclone systems can quickly lift air pollutants, such as BC, up to the free troposphere, as well as extend their lifetimes and further affect the regional atmospheric environment and climate.

Presence of nanoplastics in rural and remote surface waters

It is now established that microplastics are a pervasive presence in aquatic and terrestrial ecosystems. The same is assumed to be true for nanoplastics but data are lacking due to technical difficulties associated with sample analysis. Here, we measured nanoplastics in waterbodies at two contrasting sites: remote Siberian Arctic tundra and a forest landscape in southern Sweden. Nanoplastics were detected in all sampled Swedish lakes (n = 7) and streams (n = 4) (mean concentration = 563 µg l− 1) and four polymer types were identified. In Siberia nanoplastics were detected in 7/12 sampled lakes, ponds and surface flooding, but only two polymer types were detected and concentrations were lower (mean 51 µg l− 1). Based on back-calculation of air mass trajectories, we infer that nanoplastics arrive at both sites by aerial deposition from local and regional sources. Our results suggest that nanoplastics may be a near-ubiquitous presence even in remote ecosystems.